Python quasar colours

Resolution #11 was to learn python - last week I read all about tuples and lists and dictionaries and functions, then this week I used some python tools written by one of our other postdocs (Matt) to calculate the expected colours of multiply-imaged quasars we might find in the PS1 survey. It seems that the most time-consuming part of programming in python is tracking down the library function that does exactly what you want in one line!

"Colour" is a technical term in optical astronomy - its roughly the logarithm of the ratio of the brightnesses of an object seen through two different filters. PS1 has 5 filters, g, r, i, z, and y (blue-green, red, and three near infra-red filters), which gives 4 colours. I plotted the predicted colours against each other in pairs, with points coloured according to their disance from us (actually their redshift). You can see that (g-r) is the most informative for telling us if the quasar is very distant. You can also see that the actual brightness of the quasar is not very helpful, which I thought was quite surprising.